Eosinophil Count: Explanation & Risks

Eosinophil Count

What Is an Eosinophil Count?


  1. An eosinophil is a type of white blood cell.
  2. An eosinophil count is a type of blood test that measures the quantity of eosinophils in your body.
  3. A normal blood sample reading will show fewer than 350 eosinophil cells per microliter of blood.

White blood cells are an important part of your body’s immune system. They’re vital to protecting you from invading bacteria or parasites. Your body is host to five different kinds of white blood cells. Your bone marrow makes all five kinds of white blood cells. 

Each white blood cell lives anywhere from several hours to 12 days and then a new one replaces it. The average lifespan of a white blood cell is five days. How many white blood cells and which type you have in your body can give doctors a better understanding of your health. Elevated levels of white blood cells in your blood are a good indicator that you have an illness or infection. Elevated levels mean your body is sending more and more white blood cells to fight off infections.

An eosinophil count is a type of blood test that measures the quantity of eosinophils in your body. An eosinophil is a type of white blood cell. An eosinophil count typically helps your doctor confirm a diagnosis rather than make a diagnosis.

Eosinophils have two distinct functions in your immune system. They destroy invading germs like viruses, bacteria, or parasites such as Giardia and pinworm. Eosinophils also create an inflammatory response, especially if an allergy is involved. 

Inflammation is neither good nor bad. It helps isolate and control the immune response at the site of an infection, but it also damages the tissue around it. Allergies are immune responses that often involve chronic inflammation. Eosinophils play a significant role in the inflammation related to allergies and asthma. 

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Why Do I Need an Eosinophil Count?


Your doctor may recommend an eosinophil count if you already had a white blood count differential and the results were abnormal. A white blood count differential test determines the percentage of each kind of white blood cell present in your blood. This test will show if you have an abnormally high or low count and if you have abnormal cells that occur with various diseases.

Your doctor may also order this test to help confirm the diagnosis of certain diseases or conditions, such as: 

  • an extreme allergic reaction
  • the initial stages of Cushing’s disease, which is a disorder caused by too much of the steroid hormone cortisol
  • a parasitic infection

How Do I Prepare for an Eosinophil Count?

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There are no special preparations necessary for this test. You should inform your doctor if you’re taking any blood-thinning drugs such as warfarin (Coumadin). Your doctor may advise you to stop taking certain medications.

Medications that may cause you to have an increased eosinophil count include: 

  • appetite suppressants
  • interferon, which is a drug that helps treat infection
  • some antibiotics
  • laxatives that contain psyllium
  • tranquilizers 

Be sure to mention any current medication you’re taking to your doctor before the test.

What Happens During an Eosinophil Count?


A healthcare provider will take a sample of blood from your arm by following these steps:

  1. First, they’ll clean the site with a swab of rubbing alcohol.
  2. They’ll then insert a needle into your vein and attach a tube to fill with blood.
  3. After drawing enough blood, they’ll remove the needle and cover the site with a bandage.
  4. They’ll then send the blood sample to a laboratory for analysis.

What Do the Results Mean?


Normal Results 

A normal blood sample reading will show fewer than 350 eosinophil cells per microliter of blood.

Abnormal Results 

If you have over 350 eosinophil cells per microliter of blood, then it indicates you have a disorder known as eosinophilia. This can be due to any of the following:

  • an allergic reaction to parasitic worms
  • an autoimmune disease
  • eczema
  • asthma
  • seasonal allergies
  • leukemia
  • ulcerative colitis
  • scarlet fever
  • lupus
  • Crohn’s disease 

An abnormally low eosinophil count can be the result of intoxication from alcohol or excessive production of cortisol, which is a steroid produced naturally in the body.

What Are the Complications Associated with an Eosinophil Count?

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An eosinophil count uses a standard blood draw, which you have likely had many times in your life. 

As with any blood test, there are minimal risks of experiencing minor bruising at the needle site. In rare cases, the vein may become swollen after blood is drawn. This is called phlebitis. You can treat this condition by applying a warm compress several times each day. If this isn’t effective, you should consult your doctor.

Excessive bleeding could be a problem if you have a bleeding disorder or you take blood-thinning medication such as warfarin (Coumadin) or aspirin. This requires immediate medical attention.

What Happens After an Eosinophil Count?

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If you have an allergy or parasitic infection, your doctor will prescribe a short-term treatment to alleviate symptoms and revert your white blood cell count to normal. 

If your eosinophil count indicates an autoimmune disease, your doctor may want to conduct more tests to determine which type of diseases you have. They may then prescribe corticosteroids. 

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You Asked, We Answered

  • What are the warning signs that you may need an eosinophil count?
  • Any sign of severe allergies can indicate that you need to have your eosinophil count checked. These signs include: sneezing and a blocked, itchy, or runny nose (nasal rhinitis); burning or itchy and red eyes (conjunctivitis); shortness of breath with wheezing or persistent cough (asthma or bronchospasm); a red, itchy, and raised rash on the skin (urticaria or hives); or swelling of soft tissues, especially on the lips, tongue, or facial areas. 

    - Steve Kim, MD

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